1. Field of The Invention
The present invention relates to a rectifying system having the function to regulate the output voltage of a magnet-type AC generator used for charging a battery such as one mounted on an automotive vehicle.
2. Description of The Prior Art
A conventional winding-type AC generator has an armature winding that is connected in multiple phases,or is Y-connected in three phases, for example. In this kind of generator, the neutral point of the armature winding is connected to at least one of the DC output terminals of a three-phase full-wave rectifier circuit through a pair of diodes at a neutral point. This allows the third high-harmonic voltage generated at the neutral point is taken out by full-wave rectification through a neutral-point diode in order to increase the rectified output current, as is well known (eg. see Japanese Pat. Publication No. 4451/65).
This well-known circuit has been used with an alternator for charging the automotive battery. This alternator comprises an electromagnet and a slip ring in the field section thereof making up a rotor.
For regulating the output voltage of the alternator, the voltage applied to the electromagnet through the slip ring is regulated through a voltage regulator.
The regulator operates in such a manner that a transistor continues to turn on and off to adjust the effective value of the voltage applied to the electromagnet.
The present trend, however, is toward "magnetization" of the alternator, that is, the electromagnet of the field section is being replaced by a permanent magnet. Since the magnetic fluxes of the field section cannot be controlled, however, the phase of the output voltage is required to be controlled by a thyristor.
For this purpose, at least three of the six diodes in Gratz connection for full-wave rectifying the three-phase AC output, for instance, is are required to be replaced by thyristors. Although the phase of the three-phase AC output is able to be controlled in this way, the half-wave portion of the neutral-point output would be applied to the battery without being phase-controlled at all through one of the neutral-point diodes and the Gratz-connected diodes if a pair of neutral-point diodes are connected to the neutral point as in the prior art disclosed in Japanese Pat. Publication No. 4451/65.
In such a case, the battery voltage does not increase excessively while the magnet-type AC generator is running at low speeds. When the generator speed increases to a point where a high voltage is generated at the neutral point, however, the battery voltage exceeds a target value by a great margin, thereby overcharging the battery. As a result, the idea of increasing the charging capacity of the battery by taking out the neutral-point output through a diode connected at a neutral point has been unavoidably discarded.